Two existing CDMA standards include UMTS, also referred to as WCDMA and 3 GPP, and CDMA 2000 also referred to as 3GPP-2.
Referring firstly to FIG. 1, shown is an example of a conventional WCDMA (wideband code division multiple access) downlink structure. This consists of a number of channels all of which are separated using Walsh codes. These are shown to include a primary SCH (synchronization channel) 10, secondary SCH 12, pilot channel CPICH (common pilot channel) 14 and a dedicated channel 16, for example a voice channel. All of these are typically covered with a high spreading factor, for example 64. There is a 10 ms frame containing 15 slots each 10/15 ms in duration. Also shown is the WDCMA HSDPA (high speed data packet access) channel 18. This channel is used in a time division multiple access fashion, with two millisecond slots being assigned on a scheduled basis to different users. One such 2 ms slot 26 is shown to contain three 10/15 ms slots 20, 22, 24. This provides a fairly high bandwidth channel. This is still transmitted using CDMA, but typically the spreading factor is lower than that used for the other channels, and it might for example be 16 or 32. All of the channels are covered with a common PN code. Advantageously, this structure is backwards compatible with existing UMTS terminals which do note use the WCDMA HSDPA channel. The WCDMA HSDPA is included in the so called EV/DV evolution.
Referring now to FIG. 14, shown as the structure of the conventional CDMA2000 release A/B/C channel structure. This channel structure includes release A\B channels 200 and release-C new channels 202. The release A\B channels 200 include a CDM pilot 204, a synch channel 206, broadcast channel 208, paging and quick paging 210, CACH 214, F-FCH 214, F-SCH 216, F-SPDCCH 218. The release-C new channels 204 include the F-SPDCCH 218 and the F-PDCH 220. The frame structure consists of a 20 ms frame 222 divided into sixteen 1.25 ms slots 228. Each such slot is used to transmit 1536 chips. Eight such slots produce a 12288 chip transmission 230. Some of the channels are power-controlled channels as indicated at 224, and some of the channels are rate-controlled channels as indicated at 226.
For both of the above examples of existing CDMA systems, the Walsh code space available is all but depleted, and as such new methods of providing further bandwidth would be desirable.